Unsaturated polymers, such as the natural and synthetic rubbers are often reinforced with fibers or textiles made from organic or inorganic fibers. Examples of such reinforcing substrates include cords, fibers and textiles made of carbon, nylon, aramid, cotton, silk, rayon, wool, polyester, glass and steel. The unsaturated polymers include, for example, polymers made from butadiene, styrene, isoprene, isobutylene, acrylonitrile, ethylene, propylene, chloroprene, and derivatives of the same. The applications for such reinforced polymers include tires, hoses, pressure vessels, and other such fiber-reinforced articles.
It is often a problem to achieve good adhesion between the reinforcing substrate and the unsaturated polymer matrices. In the past, the adhesion problem has been addressed by use of an adhesion promoter. One such adhesion promoter is a resorcinol-formaldehyde-latex (RFL) which has been widely used and modified since its invention by Charch. Its use was taught in U.S. Pat. No. 2,211,945. As the term RFL indicates, the resin is usually resorcinol-formaldehyde (RF) copolymer. However, other resins such as acrylic polymers, phenol polysulfides, phenol-formaldehyde type polymers may be used. Examples of these are taught in U.S. Pat. No. 4,472,463; Great Britain 2,147,303, and U.S. Pat. No. 4,448,813.
The latex in the RFL system is usually butadiene/styrene/vinyl pyridine polymer. This polymer has been the industry standard since it was invented by Mighton, U.S. Pat. No. 2,561,215. The RFL is applied as a coating to the substrate, which is subsequently heat-treated to cure (i.e., "crosslink") the RFL resin. The unsaturated elastomer from the latex, however, remains uncured. The matrix elastomer is then applied to the RFL-treated substrate and the composite is subsequently cured to form the product.
The present invention provides a heretofore unknown latex composition which acts in a resin formulation as an adhesion promoter between organic substrates and unsaturated polymers. The latex can be a dispersion of a copolymer of styrene and butadiene with an amine substituted alkyl acrylate; or it can be a dispersion of a shell/core polymer where the core is a styrene/butadiene copolymer and the shell comprises a copolymer of the styrene, butadiene, and the acrylate. The composition is generally formed in an emulsion copolymerization. The composition is then used in a resin/latex formulation to form a coating of reinforcing substrates and thereby provide adhesion between the reinforcing substrate and an unsaturated polymer matrix.